This invention relates to nitrogen containing N-substituted arylamino-phenol-formaldehyde condensates, e.g. those of N-ethylaniline-phenol-formaldehyde, which have a low melt viscosity, are soluble in solvents commonly used in epoxy formulations, and are self-catalyzing curatives for epoxy resins. This latter property permits faster curing and/or curing at lower temperatures while providing adequate mix life.
It has now been found that N-substituted arylamino-phenol-formaldehyde condensates having desirable and unexpected properties can be produced by:
(A) charging to a reaction vessel a phenol and (a) one member selected from the group consisting of formaldehyde and an N-substituted arylamine, e.g. N-ethylaniline, to form a reaction mixture; subsequently
(b) charging the remaining member of said group to the reaction mixture;
(B) heating the reaction mixture until all of the formaldehyde and said arylamine have reacted and the condensate contains from about 35% to 63% by weight of phenol residue wherein
(i) the molar ratio of said phenol to formaldehyde to said arylamine is 1.5 to 4 moles of the phenol and 1.5-3 moles of formaldehyde for each mole of the arylamine;
(ii) the phenol is a member selected from the group consisting of phenol itself, an alkylphenol having from 1 to 4 carbon atoms in the alkyl group, a meta- or ortho-alkoxyphenol having from 1 to 4 carbon atoms in the alkoxy group, and mixtures thereof; and
(iii) said arylamine is a member selected from the group consisting of a mononuclear (1) or dinuclear (11) compound as represented by the following Formula I and Formula II, respectively: 
wherein R is alkyl of 1 to 4 carbon atoms, hydroxyethyl or hydroxypropyl; Rxe2x80x2 is hydrogen, methyl or ethyl in the ortho or meta position in relation to the nitrogen; and X is either a covalent bond, oxygen, sulfur, carbonyl or xe2x80x94SO2xe2x80x94. In place of the formaldehyde being substantially all formaldehyde, the above method includes the substitution of up to about 20 mole percent of the formaldehyde with an equal molar quantity of another aldehyde having from 2 to 7 carbon atoms.
The condensates of this invention have a nitrogen content of about 3.5% to about 6.5% by weight. Thus, in addition to being effective self-catalyzing curing agents for epoxy resins, the condensates of this invention also provide enhanced fire-retardant properties to epoxy compositions. Furthermore, lower concentrations of the condensates can be employed as accelerators for curing epoxy resins with phenol-formaldehyde resins as compared to the use of conventional accelerators. Condensates of this invention also provide other beneficial properties that include, but are not limited to, improved adhesion to metals, particularly copper, improved impact resistance to cured epoxy formulations, and improved moisture resistance as compared to phenol-formaldehyde novolac curing agents. The condensates of this invention are also suitable in the manufacture of molded products as well for other uses enjoyed by phenolic novolac resins.
The reaction of phenolic compounds with amines, generally secondary amines, and formaldehyde is well known and are an example of the Mannich condensation, e.g., see H. A. Bruson, C. W. McMullen, J. Am. Chem. Soc., 63, 270 (1941); M. Julia, Bull. Soc., Chim. France, 1955, 830; and R. L. Hull, J. Am. Chem. Soc., 77, 6376 (1955). However, the products of the reactions cited in the above references are oligomers as contrasted to polymers having more than 4 repeating units and may act as accelerators for epoxy reactions but not as effective curing agents. The reason for this is that the hydroxyl functionality of such materials is only about one or two which provides insufficient crosslinking as compared to conventional curing agents such as phenol-formaldehyde curing agents which have a hydroxyl functionality of at least 6. Likewise the products of substituted phenols with N-monoalkylanilines and formaldehyde(M. Miocque, J. M. Vierfond, Bull. Soc. Chem. France, 1970, 1901, or with N,N-dialkylanilines and formaldehyde (ibid, p. 1896) give monoaminomethylated products unsuitable as effective epoxy curing agents whereas the condensates of this invention produce polymers having more repeating units and viscosities of at least 700 cps at 150xc2x0 C.
U.S. Pat. No. 4,518 748 of May 21, 1985 to Haug et al. as well as U.S. Pat. No. 4,552,935 of Nov. 12, 1985 to Haug et al., show curable epoxide compositions containing condensates prepared from certain phenols, certain amines and aldehydes in an acid medium. However, only primary and tertiary amines are shown.
U.S. Pat. No. 5,569,536 of Oct. 19, 1996 to J. Hunter et al. use polyamines with primary amino end groups and further, the mole ratio of ingredients are substantially different from those of the instant invention. Furthermore, the condensates of this 536 patent cannot form significant amounts of acyclic tertiary amino linkages.
N,Nxe2x80x2-dialkylalkylene diamines can form condensates with phenol and an aldehyde. However, the alkylene group unlike the arylene group is more susceptible to thermal and flame degradation. Moreover, such condensates would be more highly basic than the condensates of the instant invention and would provide poor mix stability in formulations with epoxy resins. Basic ionization constants (pK) for highly basic amines such as N,N-dimethylbenzylamine, and N,N-dimethyl hexylamine are 9.02, and ca. 10, respectively.
Primary aliphatic or aromatic amines, unlike the N-substituted arylene amines of the instant invention, react with aldehydes to form unstable N,N-dimethylol compounds or alkyleneimines which generally are unstable and can trimerize or even polymerize (J. F. Walker, xe2x80x9cFormaldehydexe2x80x9d, 3rd ed. pp. 360-362, 370, 1964, Reinhold Publishing Corp.). Tertiary amino N,N-dialkylarylamines cannot form the tertiary amino Nxe2x80x94CH2-groups as part of a condensate. Tertiary amino groups of the instant condensates, particularly as the idealized repeating units of (Nxe2x80x94CH2-Aryl-CH2-Aryl-)n, are believed to be responsible for enhancing the flexibility/toughness of cured epoxy resins.
In Chem. Abst., 45, 2487i (1951), W. J. Burke et al., several primary amines were reacted with formaldehyde and polyhydroxy benzenes (i.e., hydroxyphenols) to give substituted benzo bis-and tris-m-oxazines.
In Chem. Abst., 47, 5408i (1953), W. J. Burke et al., 2-Naphthol was condensed with formaldehyde and aliphatic or alicyclic primary amines to give substituted naphtho m-oxazines or substituted methylene diamines, depending on reaction conditions. None of the above Burke et al. products were polymeric and none were derived from aromatic amines.
In Chem. Abst., 50, 6408i (1956) W. J. Burke et al., aromatic primary amine, 2-naphthylamine, was reacted with formaldehyde and 2-naphthol. Products of this reaction were non-polymeric being a substituted naphthol m-oxazine and a naphthylaminomethylated 2-naphthol. None of the above W. J. Burke et al. references use an N-substituted amine.
Primary aromatic amines can also be reacted with phenol and aldehydes such as formaldehyde to give benzoxazines. In the case of a diphenolic compound a primary amine and formaldehyde difunctional benzoxazines and other oligomers are formed (A. Gardziella, L. A. Pilato, A. Knop, xe2x80x9cPhenolic Resinsxe2x80x9d, pp. 57-58, 1999, Springer-Verlag, N.Y.). Benzoxazines, unlike the condensates of the instant invention undergo facile ring opening with active hydrogen compounds including phenol and phenolic oligomers.
In one aspect, this invention is directed to N-substituted arylamino-phenol-formaldehyde condensates which are substantially free of water, contain not more than 2% by weight of a phenol and possess unobvious properties, e.g., which have the residues of an N-substituted arylamine and 1.5 to 3 moles of formaldehyde for each mole of the said arylamine, contain from about 35% to 63% by weight of phenol residue, contain at least 3.5% by weight of nitrogen, have a melt viscosity of less than 2,000 cps at 175xc2x0 C., a hydroxyl equivalent of about 195 to 220, a Methanol Tolerance of at least 40%, high solubility in organic solvents commonly used in epoxy formulations, and are self-catalyzing curatives for epoxy resins.
In another aspect, this invention is directed to an epoxy resin composition containing an N-substituted arylamino-phenol-formaldehyde condensate of this invention.
In another aspect, this invention is directed to prepregs containing compositions of an epoxy resin and an N-substituted arylamino-phenol-formaldehyde condensate of this invention.
In another aspect, this invention is directed to cured compositions comprising the N-substituted arylamino-phenol-formaldehyde condensates of this invention with epoxy resins as well as laminates containing the condensates and epoxy resins.
In yet another aspect of this invention the N-substituted arylamine-phenol-formaldehyde condensates of this invention either alone or in admixture with another epoxy curing agent and/or another fire-retardant can be used as fire-retardant curing agents for epoxy resins.
In another aspect, this invention is directed to methods for the manufacture of the N-substituted arylamino-phenol-formaldehyde condensates as well as epoxy compositions, prepregs and laminates containing the same.
In another aspect, this invention is directed to the condensates, epoxy compositions, prepregs and laminates prepared by the above described methods.